Biochemical characterization of the hippocampal and striatal Na,K-ATPase reveals striking differences in kinetic properties.
The activities and basic enzymatic properties of Na,K-ATPase were examined in synaptosomal plasma membranes (SPM) prepared from rat hippocampus and striatum. A kinetic analysis showed profound differences in apparent affinities for ATP (Km) between hippocampal (1.21 mmol/l) and striatal (0.76 mmol/l) enzyme preparations, as well as in the corresponding Vmax values. However, physiological efficiencies were almost the same. The complex pattern of dose-response curves to ouabain indicated the presence of two high-affinity forms of Na,K-ATPase in the striatum ("very high-": Ki = 3.73 x 10(-8) mol/l and "high-": Ki = 4.21 x 10(-5) mol/l), and one high affinity form in the hippocampus (Ki = 6.6 x 10(-7) mol/l). In addition, both SPM preparations contained one low affinity form with similar Ki. The "very high-affinity" form had positive cooperativity for ouabain inhibition of Na,K-ATPase activity, in contrast to "high" and "low-affinity" forms, which exhibited negative cooperativity. The respective contributions of ouabain-sensitive forms to the total activity were estimated as 22%, 46%, 19% for the striatum and 36%, 45% for the hippocampus. These data clearly demonstrate striking differences in kinetic properties of the hippocampal and striatal Na,K-ATPase that may be due to the isoenzyme diversity and adaptation to specific physiological demands of the examined rat brain regions.
Peković
S
S
Laboratory for Molecular Biology and Endocrinology, Vinca Institute for Nuclear Sciences, Belgrade, Yugoslavia.
Nedeljković
N
N
Nikezić
G
G
Horvat
A
A
Stojiljković
M
M
Rakić
L
L
Martinović
J V
JV
D000818:Animals; D001665:Binding Sites / Q000187:drug effects; D003342:Corpus Striatum / Q000201:enzymology*; D004789:Enzyme Activation / Q000187:drug effects; D005260:Female; D006624:Hippocampus / Q000201:enzymology*; D007527:Isoenzymes / Q000378:metabolism; D007700:Kinetics; D010042:Ouabain / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism*
D007527:Isoenzymes; D010042:Ouabain; D000254:Sodium-Potassium-Exchanging ATPase